Effects of climate and ocean conditions on the marine survival of Irish salmon (Salmo salar, L.).

摘要

This dissertation investigates the role of climate and ocean conditions on the marine survival of Atlantic salmon. The overall objective was to identify the relevant environmental variables controlling salmon marine survival, in order to establish predictive models of marine recruitment. These models are required to improve the management process of the Irish and European salmon resources.; I first explored the levels of synchrony in the marine survival of European salmon, in order to assemble evidence on the spatial scale of the processes controlling survival. I demonstrate that these levels of synchrony are low and I conclude that large scale events are not directly exerting a control on the rates of salmon survival, perhaps indicating the presence of several intermediary processes.; Using information from a scale analysis of a monitored Irish population, I then explore the hypothesis that marine survival is linked to marine growth. I present evidence that the level of marine recruitment of 1 SW salmon is linked to growth during the marine residency, and that decreasing growth over the last 30 years explains the observed decrease in salmon recruitment.; Finally, I explore the role of several environmental variables on salmon marine survival, by constructing semi-parametric models (GAMs) of marine survival for wild and hatchery Irish populations. These models explain an important part of the inter-annual variability in survival and provide a capability to forecast survival. These models also help to identify the role of specific variables, more specifically the North Atlantic Oscillation, sea surface temperatures, and the abundance of zooplankton, to explain the variations in survival.; I conclude that the changes in climate in the northeast Atlantic have affected the salmon via bottom-up effect, by affecting the abundance, distribution and phenology of key zooplankton species in the northern North Sea and southern Norwegian Sea.